Viewing angle

LCD monitors are usually advertised as having a viewing angle of
somewhere between 140 and 165 degrees. This means that you can still see
what's on the display if you are looking at it at 70 to 83 degrees from the
side. However, most of the time, you will be sitting roughly straight in
front of the screen, which means that you are looking at 0 degrees to the
center of the screen and at most 45 degrees to the sides. Compared to the
advertised viewing angle, it is much more relevant that the display does not
change brightness or color in the corners. The following test images are
best viewed from a distance of approximately equal to the diagonal of the
display.

Viewing angle and gamma

The word 'lagom' on this image should blend in with the background
everywhere; otherwise the gamma curve of your monitor is dependent on the
viewing angle, which is the case with most displays based on TN technology.
Typically, the letters appear blue-green at the top and red at the bottom.
Note: this test image requires that the screen operates in its native
resolution and that the image is not scaled.

www.lagom.nl/lcd-test

Viewing angle and brightness

Each of the following images
contains only a single color that fills the whole plane. When your eyes are
close to the screen, the color in the middle and close to the edges should
look the same.

This first one, in purple, is the most revealing one on my display. The
color appears to vary between lavender and pale blue.

www.lagom.nl/lcd-test

The red surface may appear to vary between deep red and purplish-pinkish
red

www.lagom.nl/lcd-test

The green image may appear to vary between pure green and yellowish
green.

www.lagom.nl/lcd-test

This surface is pure blue and will probably only show brightness
differences, rather than color differences.

The second photo is the same monitor, but taken from twice the
screen diagonal. Slightly better, but imagine that you are trying to adjust
the color balance of a photo on a screen like that...

Unfortunately, you can't change anything about the angle dependence of a
monitor, except by replacing it by a better monitor. Some newer TN-based
monitors are a bit better than the sample above, but a monitor with a
MVA/PVA or IPS matrix can perform vastly better than this.

Plain colors

When looked at from a close distance (i.e. at a distance roughly
equal to the monitor diagonal size), the purple
surface might look like this. The color changes vertically from
pinkish to blue and is darker in the edges compared to the
center. This is a typical behavior of TN (twisted nematic) LCD
screens.